Gyroscopically operated measuring instrument



June 9, 1953 T. w. KENYON 2,641,134

GYROSCOPICALLY OPERATED MESURING INSTRUMENT El* 'www ATTORNEYS June 9,1953 T W, KENYON 2,641,134

GYROSCOPICALLY OPERATED MEASURING INSTRUMENT Filed July 6, 1950 5Sheets-Sheet 2 ATTORNEYS,

T. W. KENYON GYROSCOPICALLY OPERATED MEASURING INSTRUMENT `lune 9, 19533 Sheets-Sheet 5 Filed July 6, 1950 Patented June 9, 1 953GYROSCOPICALLY OPERATED MEASURING INSTRUMENT Theodore W. Kenyon,Huntington, N. Y., assignor to Gyromechanisms, Inc., a corporation ofNew York Application July 6, 1950, Serial No. 172,273

(Cl. M -5.6)

'7 Claims.

This invention relates to gyroscopically operated measuring instrumentsand more particularly to rate gyros useful in aircraft, marine and landvehicles.

Objects and features of the invention are to provide instruments of thiskind that have high sensitivity, wide useful range, high accuracy andextremely high natural frequency and wherein a gyro and gimbal of veryfavorable inertia ratio are coupled to a continuously linear signalpick-off which in one example is frictionless.

In the rate gyro constituting this invention, the driving motor isseparated from the gyro wheel so that all possible non-spinning mass iseliminated from the suspended member. Gyro wheel drive from the drivingmotor is accomplished by use of a remote drive, and a remote driveconnecting means including a ball and pin assembly at the intersectionof the wheel and gimbal axes. This remote drive as a further advantageof permitting the use of a simple but effective clutch in the connectingmeans between the motor shaft and the gyro wheel. With this arrangementthe small synchronous driving motor is not required to provide torquefor immediate starting of the gyro wheel and can, therefore, come up tolock-in speed almost immediately. The gyro wheel driven through theclutch attains synchronous speed shortly thereafter (withinapproximately 90 seconds). A direct coupling on the other hand, wouldrequire a driving motor at least three times as powerful.

Other objects and features of the invention are the provision ofstructure enabling the separation of the driving motor from the gyrowheel to eliminate all possible non-spinning mass from the gyro wheeland the utilization of clutch coupling between the gyro wheel and motordriving shaft whereby a motor of approximately 1/3 the power necessaryfor direct drive can be utilized effectively.

Another object and feature of the invention is the provision ofstructure providing high sensitivity and a natural frequency that ishigh.

The performance of a gyro embodying the features of this invention canbest be explained in terms of fundamental theory. The deectionsensitivity of a rate gyro is given by:

where:

S=deflection sensitivity pzdeection angle of gimbal Q=1neasured turnrate Ip=polar moment of inertia wp=angular velocity about spin axislc--stiffness about deiiection axis (This equation is only approximatewhere the deflection angles are large.)

The natural frequency of the gyro is a function of the ratio of thestiffness to the inertia about the deiiection axis; thus:

l lc ffl-; (2) where:

fn=undamped natural frequency I1=inertia of gyro wheel and gimbal asmeasured about gimbal axis The above two equations show theincompatibility of high sensitivity and high natural frequency. Anincrease in stiffness lc aimed at increasing the natural frequency mustnecessarily lower the deflection sensitivity.

Since the stiffness lc is a dependent variable adjusted according to thedesign requirements, it can be eliminated in a simultaneous solution ofthe above two equations to obtain an expression relating frequency andsensitivity.

I D w is high for the gyro of this invention, it can be seen that thenatural frequency for the design maximum rate of turn is also very high.

Other objects and novel features will become apparent from the followingspecification and the accompanying drawings wherein Fig. 1 is a top planview of a rate gyro embodying the invention;

Fig. 2 is an elevational view of the rate gyro;

Fig. 3 is a transverse vertical section on an enlarged scale taken alongline 3 3 of Fig. l;

Fig. 4 is an elevational view similar to Fig. 2 with a part of thecasing broken away to illustrate details of construction;

Fig. 5 is a transverse horizontal section taken along line 5-5 of Fig.3;

Fig. 6 is a transverse horizontal section taken along line 6-6 of Fig.4;

Fig. 7 is a vertical section taken along line 'l-'l of Fig. 6;

Fig. 8 is a vertical section of a ball and pin assembly element used inthe rate gyro of the invention;

Fig. 9 is a transverse longitudinal section of a modified form of rategyro, and.

Fig. 10 is a partially diagrammatic elevation of a modified pick-offsystem that may be used with either modification in place of that shownin Figs. 3, 4, 6 and 7.

Referring to the drawing, II] denotes a substantially cup-shaped base inwhich in its upstanding wall I I at diametrically opposite points, thestuds i2, I3 are threadedly mountedL and conveniently locked in mountedposition by the set screws I4, I5. A gimbal frame IB is rotativelysupported on the studs I2, .I3 by ball bearings I'I, I8. This gimbalframe has a bottom wall I9 provided with a journal ZI) which receives aball bearing support 2l which latter carries a shaft section 22. Thisshaft section 22 has a recess 23 at one end and vertical slots 24 and24a at diametrically opposite points in the wall defining the recess Agyro wheel 25 is frictionally mounted on the shaft section 22 forrotation about the axis of shaft section 22 on the ball bearing support2i. A second shaft section 26 axially alined with the shaft section 22is fitted within the center bore of the gyro wheel 25. This shaftsection 25 is tubular and extends upwardly of the wheel 25 into a ballbearing support 2l carried by a threaded plug 2-8. The plug 28 isthreadedly engaged in a threaded hole 29 of a transversely extending topplate 3i) spanning the gimbal frame E5. The plate 33 is secured as bybolts or pins 3! to the side wall of the frame I6. A locking nut 32serves to lock the plug 28 in any adjusted position to prevent axialdisplacement of wheel 25.

A well 34 is provided in the bottom of frame IE! of substantially largerdimensions than those of the journal 2E) so as to permit free pivotingof the gimbal frame I6 on the stub shafts I2 and I3.

A cover plate 35 is secured as by bolts 31 on the top edge of the frameIIJ. A centralized journal 55 extends upwardly from `the plate 35. Aninverted cup-shaped shell or cap 35 is secured to the upper face ofplate 36 being centralized relative to the journal 38 by an upstandingannular ilange protruding from the upper face of plate 36. The shell orcap 39 has an inwardly extending boss 4I axially Valined with journal38. The two bosses 35 and 4I together with ball'bearings 42, 43rotatively support the rotor shaft 44 of an electric motor M. In thisembodiment the motor is preferably an A. C. three phase motor whose eldcoils (not shown in detail) are supported within shell 39 in appropriaterelationship to the rotor. The rotor shaft 44 extends downwardly throughthe boss 38 and has a sleeve 45 secured thereto. Shaft 44 and its sleeve45 are axially alined with the shaft sections 22 and 25 but spaced fromthe latter as shown. The sleeve 45 has a reduced diametered end portion46.

A special remote drive connection is .utilized to couple rotor shaft 44and its sleeve 45 to the shaft section 22. This arrangement includes aball and pin assembly and simple clutch providing thereby a remote drivefor the gyro wheel 25 which has among its advantages the elimination ofall possible non-spinning mass from the gyro wheel parts and alsopermitsAuse of a driving motor substantially three times Vless powerful thanwhat would be .required if direct coupling were employed.

The ball and pin assembly comprises a pin member 48 of substantiallysmaller diameter than the bore of the shaft section 26 which extendstherethrough and terminates in a ball 49 which is received in the recess23 of the shaft member 22. The ball is dimensioned so that its centerlies substantially at the intersection of the axes of the stub shafts I2and I3 and the vertical axes of shaft sections 22 and 23. Lateral pins50 and 5I alined with the axes of stub shafts I2 and E3 when ball 49 isin recess 23 engage the respective vertical slots 24 and 24a to providea universal joint coupling between member 48 and shaft section 22substantially at the intersection of the gimbal frame and. gyro wheelaxes.

A head 53 is provided at the outer end of pin 48. This head is ofslightly smaller external diameter than the inner diameter of portion 4Gof sleeve 45 and extends into said portion. A coil spring 54 infrictional engagement with the inner surface of portion 45, alsosurrounds the head 53 within said portion 46 and has one end 54'positively engaged in a slot 55 in the top of head 53. This spring 54and its relative arrangement with respect to head '53 and sleeve portion46, provides a simple, effective clutch between the rotor shaft 44 andthe gyro wheel 25. With this arrangement, the small synchronous motor isnot required to provide torque for immediate starting of the gyro wheel25 but instead can come up to lock in speed immediately because ofrelative slip resulting from tightening of the spring when startingtorque is applied to the rotor shaft 44. This slip continues at adiminishing rate until the gyro rotor 25 driven through the plutchcoupling at spring 54 attains synchronous speed with the rotor shaft 44shortly thereafter, usually within seconds. At synchronous speed thespring 54 is fully expanded and in full frictional engagement with theinner surface of portion 45 of sleeve 45 providing effective synchronousspeed drive of gyro wheel 25 through said spring and the ball and pincoupling with shaft portion 22.

A pair of oppositely-located, upstanding vanes 53, 59 are secured to thetop face of cover plate 30 as by bolts 60. These vanes extend upwardlythrough respective slots 6I, 62, tapering toward their upper ends whichterminate above the level of the top face of the shell 39. Insulatingblocks 53, 54 are secured to the respective vanes 58, 59 at their upperends and a metallic cross piece 65 extends transversely andsubstantially horizontally between the blocks 63, 64 being secured toeach as by bolts 65.

An insulating disc 5'! vis secured to the top face of shell 39. A pairof spaced apart support blocks 68, 69 of insulating material are securedto the top face of disc 61. These blocks 68, 69 extend in parallelismwith the cross bar or piece 65. A pair of metallic bars l0, 'II aresecured to the respective blocks 68, 59. These bars have the respectivelateral flanges 10a, IIa which are positioned to underlie the cross bar65 being spaced apart throughout their lengths. Plates "I2, I3 aresecured to the bars 1G, II and are dimensioned to overlie the respectiveflanges 10a, lla above the cross piece 65 being spaced apart from thelatter. The respective plates 12, I3 and flanges 10a, 'Ila define fixedplates of tWo variable electrical condensers C and Ca. The cross piece65 constitutes a movable condenser plate which is movable substantiallylaterally in the spaces defined between the fixed plates to provide saidvariable condensers C and Ca whose capacities are varied by movementofthe cross vpiecel5 rela,-

tive to the respective pairs of fixed plates dened respectively byflange a and plate 'l2 and flange 'llc and plate T3. 'I'he xed platesand the movable plate of these two condensers C and Ca are connected inelectrical circuits as the controls for rate indicators from whichreadings may be taken. These electrical circuits which do not form partof the present invention are not shown herein.

One of the two vanes, in this embodiment the vane 58, is provided withspring restraints. As shown a pair of springs '15, 16 are securedadjacent opposite side edges to the vane 58 and to respective fixedposts or members 11, 78 secured to the plate 35. These springs 15, 'I6act oppositely on the vane 58 tending to centralize it and in additionprovide the stiffness factor lc about the deflection axis referred to inthe formulae hereinbefore set forth. These springs which are adjustableor replaceable as required act, in the embodiment shown, to provide anyfull scale rate measurement up to 60,000 degrees per minute (17.5radians per second) and can measure down to 0.5 degree per minute in thelower ranges. Typical values are given below maximum values at 0.75degree deflection.

A bimetallic spring finger 80 is secured at 8| to the plate 36 and has asurface 82 in proximate engagement with a surface 83 on the bane 58. Aviscous fluid 84 such as oil or other suitable viscous material having aviscosity number of the order of approximately 200,000 centistokes isinterposed in the small gap between the two surfaces. At least one suchviscous material is one selected from organo-silicon oxide polymers madeby combining silicon dioxide with methyl or ethyl groups of moleculesderived from alcohols or with ethylene chloride or phenol. Both straightchain o1- ring type, organic molecules may be used with silicon dioxideresulting in products of various properties. Such materials all arecharacterized by their temperature stability, inertness, waterproofnessand excellent dielectric properties. The selected of these materialsparticularly suitable has a viscosity number of the order of 200,000centistokes and is a product of Dow Corning Corporation of Midland,Michigan and is characterized by it as Silicone D. H. 200. It is to beunderstood that other viscous materials having similar properties can beemployed. The bimetallic strips of finger 80 are so designed that thegap between its surface 82 and surface 83 is varied inversely withtemperature thus compensating for the change in viscosity of the dampingfluid. By this means the damping is kept constant over a widetemperature range. The bimetallic nger 80 with the surfaces 82 and 83and the viscous material 84 is commonly known as a constant viscousdamping arrangement.

The leads (not shown) for supplying electric current to the motor areconnected to terminals T extending from a terminal block 85 supportedfrom the insulating plate or disc 61. This block 85 also carries otherterminals connected in the electric circuits of the condensers C and Ca.An enclosing casing 86 encases the entire mechanism described. In theembodiment shown this casing has substantially cylindrical shapeflttingaround the periphery of the base I0 with its lower edge engagingv anannular Vbead or flange I0a of the base l0. A sealing ring 88 ofcompressible material such as rubber is positioned within an annulargroove 89 in base |0 and acts to Yseal the lower end of casing 86 andits contents. The top 90 of the casing has an opening 90a through whichthe terminals project. The block has a groove 9| containing a sealingring 92 of material similar to that of ring 88. This ring 92 iscompressed by a clamping ring 93 and screws 94 to seal the casingcontents from atmosphere about the opening 90. The air content of casing86 may be evacuated or replaced by inert gas so that the mechanismcontents of casing 86 will operate either in vacuo or in an inert gasand will not be subject to action of moisture or to variations inatmospheric environment.

Access for repair or replacement of posts is provided by theremovability of the casing 86 on the removal of the screws 94. Electriccircuit connections are made available through the terminal prongsprotruding from opening a.

Modification Where it is desirable to have a rate gyro responsive alongmore than a single parameter, for example two parameters at right anglesto each other, the necessary structure can all be provided within asingle enclosure and using a single motor. Such a construction isillustrated in Fig. 9 hereof.

In Fig. 9, H0 denotes a substantially cupshaped base which in its sidewall I at diametrically opposite points, the studs H2, H3 are threadedlymounted and conveniently locked in mounted position by the set screwsH4, H5. A gimbal frame H6 is rotatively supported on the studs H2, H3 byball bearings HT, H8. This frame I6 has a wall 9 provided with a journal|28 which receives a ball bearing support |2| which latter carries ashaft section |22. This shaft section |22 has a recess |23 at one endand longitudinal slots |24 and |2la at diametrically opposite points inthe wall defining the recess |23. A gyro wheel |25 is frictionallymounted on the shaft section |22 for rotation about the axis 0f shaftsection |22 on the ball bearing support |2I. A second shaft section |26alined with the shaft section |22 is tted within the center bore 0f thegyro wheel |25. This section |26 is tubular and extends outwardly of thewheel |25 into a ball bearing support |21 carried by a threaded plug|28. The plug |28 is threadedly engaged in a threaded hole |29 of atransversely extending plate |30 spanning the gimbal frame H6. The plate|30 is secured as by bolts or pins |3|, |60 to the side wall of gimbalframe H6. A locking nut |32 serves to lock the plug |28 in adjustedposition to prevent axial shift of wheel |25. A well |34 is provided inthe wall of frame H0 of substantially larger dimensions than those ofthe journal |20 so as to permit free pivoting of the gimbal frame ||6 onthe stub shafts H2, H3. A plate |36 is secured as by bolts |31 to theedge of the side walls of frame H0. A centralized journal |38 extendsoutwardly of the plate |36.

A second substantially cup-shaped base Illa is axially alined with thebase l I0. In its side wall |||a this base carries studs (not shown)similar to the studs H2, H3 and similarly mounted on ball bearingssimilar tothe ball bearings -II1, I I8 -Which'rotatively support agimbal frame |611 'forrotation on an-axisat yright angles to the axis ofstuds II`2, II3. The gimbalframe II6a has a wall I |9111'provided with ajournal |2011 -which receives a -ball bearing support I2Ia which Alattercarries `a shaft section |2211. This shaft section -I2-2a'has-a recess|2311 at one `endrand longitudinal slots (not shown) Vdiametricallyopposite points in the fwallfdeningirecess |2311 similarto slots |124,|2411. jAgyro wheel |2511 is frictionally mounted fon the shaftl.section I22a'ffor rotation about the axis .of shaft 'section |2211-onthe ball bearing support -I-2|11. vA -second shaft section |2611. alined4with the shaft section |2211 is fitted within the vcenter bore of theVgyro wheel |2511. This section |2611 is tubular and Vextends`outwardlylofthewheel |a-into a ball bearing support V|2111 carriedbyathreaded plug |2811. The plug |2611 is threadedly engaged in a threadedhole :|2911 of atransversely'extending plate |3011 spanning thegimbalframe H611. The plate |3011 is secured aslby lbolts or pins(notrshown) similar to the .pins I3-I to the side wallsfof the gimbalframe H611. JA locking nut I32a serves to lock the plug |2811 i-inadjusted :position to prevent axial shift of fthe Vgyro wheel -|2511. lAvwell |34a is provided in the wall Vof frame I |011 of substantiallylarger dimensions than those of the journal 'I2'011-soasto permit"freepivoting of the gimbal frame |I611 Von its stub shafts (not shown,Vbut similar to-stub-shafts II-2, |I3) on-an-axis'at rightanglestothatofthegimbalframe II6. /A plate lI3611-is1secured asbyfbolts |3111tothefedge of thesidewalls-offrame'|1011 This p1ate-|36a is spaced fromthe similar plate |36. The centralizedjourn'als '|38, "I3811extendtoward each other fromthe faces ofplates -`|36, I36a. A shell |39 issecured tothe two plates |36, |3611 being centralize'd-and axiallyalined-with-the shaft sections |22, |26, |2211, |2611 vby the facingprotruding bosses`I40, |4011-on the respectivejplates |36, I36a. Ballbearings |4211, |4311 are mounted in the respective-journals |38, |3811and rotatively support oppositelyextendingends of |44 and4|44a a rotorshaft of an electric'motor M11. In this-embodiment the motor M11 ispreferably an A. C. three phase -motor whose field-coils (not-shown indetail) Aare supported within theshell |39 inappropriate relationship tothe rotor. The rotor shaftends |44, |4411 extend respectivelyT outwardlythrough-the journals |38, |3811 andhavefrespective'sleeves |45, |4511secured-thereto. kRotor shaft ends |44, I4411and s1eeves-|45, |4511 -areaxially'alined withithe shaft sections |22, lI 2`6-and |2211, |2611 butspaced from the latter asshown.

Special 'coupling arrangements between y'the rotorshaftends |44, |4411and respective shaft sections |22, |2211 are utilized. 'These vcouplingarrangements are substantially identical with the coupling arrangementdescribedin the rst modication. Each includes 'a balland'pin assemblyand-a simple clutch providing thereby aremote drive 'for the twogyro'wheels -|25 and |2511 from thecommonmotor Mawhichhas among its`advantagesthe elimination of'all possible non-spinning mass from `thegyro wheels and associated parts and alsopermits the use of a commondriving motor.

vThe'ball and pin assemblies vareidentical Vand hence only'thatassociated with rotor shaft end |44 Ais described. The similarpartsassociated with rotor shaft end |4411 are showninthe drawing'atth'e leftof Fig.'9 and'bear the's'am'ereference Ycharacters with `'the addedsubscript a.

lhe'ball and pin assembly associated with rotor shaft end |44 comprisesa pin member |48 of substantially smaller diameter than the bore of theshaft section I=26 which extends therethrough and terminates in a ball|49 which is received in Vthe Srecess |23 of the vshaft member `|22. TheAball #|49 lis dimensioned so that its center lies substantially at theintersection of the axes of stub shafts |I2 and II3 and the axes ofshaft `sections |22, |23. kLateral pins |50, I5I alined iwiththe axesofstub shafts II2, I|3 vengage the :respective slots |24, |2411 to providea universal joint coupling lbetween pin member |48 and shaft section |22vsubstantially at the intersection o'f the gimbal frameaxis of rotationand that.of1the gyro Wheelaxis.

A head :|53 is provided-at the other end of the pin |48. Thisfhead is'of slightly smaller external diameter than'the inner diameter ofvsleeve |45 andextendsinto the latter. A coil spring |54 in frictionalengagement with the inner surface of sleeve vI45.also.surrounds the head|53 and vhas one end |54' positively fengaged in a slot .|55 in the-topof head |53. This spring and its relative arrangement Withrespect to thehead |53 and sleeve |45 provides a simple, effective clutch be-.tweenrthe Vrotor shaftend |44 and the gyro wheel iI25 vprovidingIallthe advantages noted of the similarclutch coupling described -as tothe first modification 'and operating in the same Way as theredescribed.

The take off mechanisms for communicating positional change of thevehicle as induced by lthe relative positions of the gimbal frames ofvthe two gyro wheels |25 and |26 may be similar .to the 4capacity takeoilE systems described for the iirst modification. AIn the alternative,Vand as lshown in Figs. 9 and l0 modied forms of takeoff mechanisms maybe employed.

The modified take-.off mechanism is shown in Fig. \9 with respect to thegimbal frame I.I6 only. An identical Vtype of such `take-off mechanism(notshown in detail) is -used for the girnbal frame II6a. As seeninligs. 9.and 10 the takeoff mechanism includes a vane |58 secured totheface ofplate |30 as by bolts |60. This vane I58.at its outer edge isprovided with a segmental gear |6I. Thisgear meshes vwith a spur gear|"62 fixed toa rotatable stub shaft |63 carried in a bracket v|65attached to the shell as by rivets |66. .A pointer vane |61 lhaving acounterweight |-68`isfixedto shaft |63 and a biasing hair spring |69which .is adjustable to provide the desired stiffnessfactor k andsecured to the bracket |65 and to the pointer vane |61 acts to fbias thelatter so that its outerend |6111 lies in a definite or normal positionrelative `to an electrical resistance coil |10 shaped as .a segmentalarc lying in the arcuate path of travel of end |61 and over which saidvane may move to alter'the electric current conditions in electriccircuits (n-otyshown) connected to said coil I luto provide readingscorresponding to relative positional changes of the gimball frame I I6.'The vane |58 extends through a slot `|92 'in the partition |36. Adamping arrangement (not shown) `similar to that of the dampingarrangement 82, 84 of the first modification may be used with vane |58.Likewise, the -capacity take-off arrangement of the firstmodiicationymay if desired 'be substituted for that shown in'Figs. 9 and10.

The frames ||0 and IIIIa are joined' by `an enclosing cup-like shell|86, closed at one end |86 and secured .by its close'dend as'by screws'|81 tothe'frame Ill). vThe rim edges |88 of shel1|86 engage 'an'annular flange |69 on 'iframe Illia.

9 A `sealing ring |90 similar in function to ring 88 of the firstmodification acts to seal off the contents of shell |86. The space insaid shell may be evacuated or filled with inert gas to protect theparts therein from changes in atmospheric environment.

While specific embodiments of the invention have been described,variations in structural detail within the scope of the claims arepossible and are contemplated. There is no intention, therefore, oflimitation to the exact details shown and described.

What is claimed is:

1. A rate gyro comprising a frame, a gimbal frame supported rotativelyon a gimbal 'axis from said first-named frame, a gyro wheel rotativelysupported for rotation in the gimbal frame about an axis perpendicularto the gimbal axis, a driving motor separated from the gyro wheel toeliminate all possible non-spinning mass from the gimbal frame and thegyro wheel, remote drive connecting means between the motor and the gyrowheel, vane means mounted for movement with the gimbal frame, electricaltake off means responsive to movement of the vane means, an overallshell mounted on first named frame and enclosing the rate gyro, 4andsealing off means for protecting all contents of the shell againstchanges in external atmospheric environment.

2. A gyroscopically operated measuring instrument Icomprising a gimbalsuspended gyro wheel, a driving motor separated from the said wheel toeliminate all possible non-spinning mass from the gimbal suspended gyrowheel, remote drive connecting means between the motor and the gyrowheel, a vane connected for movement in response to gimbal movement andconstant viscous damping means arranged to act on said vane, said lastnamed means including a bimetallic spring member supported from a fixedpart of said instrument, and having a surface in proximity to a surfaceof the vane and viscous fluid interposed between the said surfaces.

3. A gyroscopically operated measuring instrument comprising a gimbalframe, supporting means for carrying said frame rotatively about agimbal axis, a gyro wheel, shaft means for rotatively supporting saidgyro wheel, said shaft means comprising a tubular shaft member and ashaft member having a recess and slots adjacent the recess, a pin memberextending through the tubular shaft member, a ball at one end of saidpin member lying in said recess, and lateral pins extending from theball into the slots, said ball and lateral pins providing a universaljoint coupling between said pin member and the shaft member having therecess, a head on said pin member, a coil spring surrounding said headand having one of its ends positively engaged with said head, a, drivingmotor separated from the gyro wheel and the gimbal frame, a. drive shaftfor said motor, a sleeve secured to said drive shaft and extending aboutsaid head and in frictional contact with said coil spring, thefrictional contact between said coil spring and said sleeve beingvariable because one end only of said coil spring is positively engagedand decreasing as said coil spring is wound by relative rotation of thesleeve and the head, thereby providing a torque limiting action betweenthe sleeve and the head.

4. A gyroscopically operated measuring instrument comprising a gimbalframe, supporting means for carrying said frame rotatively about agimbal axis, a gyro wheel, shaft means for rotatively supporting saidgyro wheel from the gimbal frame, said shaft means including a tubularshaft member and a shaft member having a recess, a pin member extendingthrough the tubular shaft member, a ball at one end of said pin memberlying in said recess, means extending from the ball for coupling thelatter to the shaft member having the recess, said ball and said lastnamed recess providing a universal joint coupling between said pinmember and the shaft member having the recess, a head on said pinmember, a coil spring surrounding said head and having one only of itsends positively engaged with said head, a driving motor separated fromthe gyro wheel and the gimbal frame, a drive shaft for said motor, asleeve secured to said drive shaft and extending about said head and infrictional contact with said coil spring, the frictional con? tactbetween said coil spring and said sleeve being Variable because one endonly of said coil spring is positively engaged and decreasing as saidcoil spring is wound by frictional action upon relative rotation of thesleeve and the head, thereby providing a torque limiting action betweenthe sleeve and the head. i

5. In a gyroscopically operated measuring instrument, a gimbal framemounted for rotative movement about a gimbal axis, a gyro wheel, shaftmeans for rotatively supporting said gyro wheel on a gyro wheel axisthat is perpendicular to the gimbal axis, said shaft means including apart having a recess, said part including oppositely located slotsadjacent the recess, a pin member extending coaxially with said shaftmeans, a head at one end of said pin member, a ball at the other end ofsaid pin member, said ball lying in said recess, lateral pins extendingfrom said ball and engaging said slots, said ball in said recess withits said lateral pins engaging in said slots providing a universal,ioint coupling between said shaft means and said pin membersubstantially at the intersection of the gimbal axis and the gvro wheelaxis, a driving motor senarated from the gyro wheel and the gimbal frameto eliminate all possible non-spinning mass from the gimbal frame andthe gyro wheel, a drive shaft for said motor, a sleeve secured to saiddrive shaft, said head on said pin member extending into said sleeve.and a coil spring surrounding said head and in frictional Contact withthe sleeve and the head. said spring having one end positively engagedwith said head, the frictional contact between said coil spring and thesleeve decreasing as the coil spring is wound by frictional action uponrelative rotation of the sleeve and the head thereby providing a torquelimiting action controlled by the coil spring.

6. A gyroscooically operated measuring instrument comprising a gimbalframe. supporting means for carrying said frame rota-tively about agimbal axis, a gyro wheel mounted for rotation in the frame about a gyrowheel axis that is perpendicular to said gimbal axis, means including ashaft member for so mounting said gyro wheel, said shaft member having arecess and slots adiacent the recess, a driving motor separated from thegyro wheel to eliminate all possible non-spinning mass from the gimbalframe and gyro wheel, a shaft for said driving motor, a sleeve securedto said shaft, a pin member having a head at one end and a ball at itsother end, a torque limiting spring coupling said head to said sleeve,said ball lying in said recess, lateral pins extending from said balland engaging in the slots of said shaft member, said recess and theslots adjacent thereto being located so that said ball and its lateral1'1 pins provide a universal joint Whose pivoting center liessubstantially at the intersection of the gimbal axis and the gyro wheelaxis.

7. A gyroscopically operated measuring instrument comprising a gimbalframe,r supporting means for carrying said frame rotatively about agimbal axis, a gyro wheel mountedfor rotation in the frame about a gyrowheel axis that is perpendicular to said gimbal axis, means including ashaft member having a recess for so mounting said gyro Wheel, a drivingmotor separated from the gyro wheel and the gimbal frame to eliminateall possible non-spinning mass from the gimbal frame and gyro Wheel, ashaft for said driving motor, a pin member having a head at one 15-References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 794,654 Anschutz-Kaempfe July 11, 1905 1,773,412 Thompson Aug.19, 193() 2,124,817 Fieux July 26, 1938 2,464,516 Kenyon Mar. 15, 1949

